The major objective of this research is to study social competence and mastery motivation in the first year of life of infants with Down syndrome and to examine the relationship between the mother-infant interaction and infant's mastery behaviors. Down syndrome infants are being studied longigudially at 3, 6 and 8 months, and a cross-sectional sample is being studied at 12 months of age. Mastery motivation is being assessed using 12 tasks developed in this laboratory. An observational system which preserves the sequence and continuity of the transactions between mother and infant is being employed to examine the mother-infant interaction. In addition, the relationship between the infants' social and mastery behaviros and specific cognitive, and temperamental variables is being examined. Infants with Down syndrome show patterns similar to normal infants in the distribution of visual attention, exploratory behavior and goal-directed behaviors in the second half of the first year; by the end of the first year, they show less persistence in and success on problem solving tasks. Patterns of mother infant interaction for the Down syndrome children differ from those of normal children.